The present invention relates to bus bars and similar high amperage conductors used in electrical circuits and in particular to a bus bar incorporating a filter against rapid voltage fluctuations.
High-power electrical equipment such as electrical motors are increasingly powered using alternating current synthesized using semiconductor devices. Such synthesized power improves the efficiency of motor operation, for example, by allowing frequency and voltage supplied to the motor to be tailored to dynamic changes in the motor's operating mode.
Desirably, the semiconductors used for power synthesis are operated in a switched mode, switching rapidly between an on-state and off-state to reduce power dissipation in the semiconductor device. Modern semiconductor devices, such as those employing silicon carbide or gallium nitride, can provide extremely rapid switch rates in the nanosecond range.
The alternating current power generated by switched semiconductors may have substantial high-frequency components caused by the rapid switching. These high-frequency components, often expressed in a rate of change of the voltage applied to the motor (dV/dT) and often termed “voltage rise time,” can damage motor insulation causing premature insulation breakdown and can induce current flow through bearing surfaces causing pitting and early bearing failure. High rise times can propagate standing waves down long motor cables as well, amplifying voltages at the motor terminals beyond their ratings.
For these reasons, standards have been developed, for example, NEMA MG1 Part 31 and Part 30, which limit the acceptable voltage rise time and peak voltages applied to certain motors. For example, these standards may limit the peak voltage applied to the motor to be equal to 3.1 times the rating of the motor voltage and the voltage rise time of the voltage applied to the motor to be greater than or equal to 0.1 microseconds, where rise time is measured between 10 percent and 90 percent of peak voltage.
These requirements often require the introduction of additional filter components positioned between the motor drive (synthesizing power for the motor) and the motor. In cases where a motor drive has been upgraded, the process of adding additional filter components may be difficult, requiring additional spacing in cabinets which were wired without contemplation of the need for filter modules.